Disclosed herein is an apparatus and method that detects carrier particles in an electrophotographic device.
Presently, electrophotographic printing machines may use a two component powder development process. The two components can include pigmented resinous powder called toner and larger granular carrier particles, such as carrier beads. Unfortunately, during the development process, the carrier beads can leave a development station, which can contaminate the printing machine. The contamination of a printing machine from the carrier beads can lead to print quality defects. Such print quality defects can include transfer deletions, print non-uniformity due to charger contamination, streaks due to cleaning failures, and ultimately, scratches in the prints from damage to the photoconductor and fuser, which can necessitate replacement of these parts. In severe cases, the development output will also fail as a developer sump falls below a minimum level. The onset for the carrier bead loss from a development subsystem is difficult to detect because it is typically very gradual and starts with a period of low rate of carrier bead loss which can then develop into a catastrophic failure leading to contamination of various printing system components. There are also situations in which this failure can occur due to aging of the carrier or because of continual high cleaning or development electric fields due to a control system compensating for extreme machine environment changes.
Typically, the failure is mitigated by limiting the toner concentration and cleaning electric field range in development as well as by adding auxiliary bead pick-off magnets downstream from development to prevent beads from contaminating the system. Unfortunately, despite the mitigation, the ultimate failure is usually detected too late, for example, when beads are felt on the output print by a user. At that point, the rest of the system is already contaminated, which critically impacts the system.
Thus, there is a need for method and apparatus that detects carrier particles emitted from a two component development system in an electrophotographic device.